Research On Key Technologies Of Wideband HF Spread Spectrum System For Data Transmission

Burst data transfer over a wideband HF channel provides subscribers an emergency communication mode. The objectives of this system are that detecting signals as precisely as possible and demodulating the information correctly over the channel with a frequency offset and a low signal to noise ratio(SNR).In this paper, it is proposed that a data transmission system over a wideband HF channel is based on Multi-ary direct sequence spread spectrum system. In this system, CRC is adopted to check the information, RS code to correct the error symbols, Walsh code to achieve spreading spectrum, M sequence to pseudo randomize the codes, a square-root raised cosine filter to restrict the spectrum of the signal, quasi-optimal non-coherent demodulation to combat the frequency offset of the channel, RAKE receiver to implement the combination of multi path signals.It is also analyzed that how the parameter of the signal frame is decided, and the generation and fast correlation of Walsh codes are studied. By the analysis and derivation of correlations between noise, useful signal and the local codes, theoretical models are established, and thus they are got that the method of setting the threshold for capturing signals and the optical scheme of spread spectrum gain.Matlab simulations on the whole baseband system approves that the performance of the system is not worse than the desired. At the end, the current implementation result of the system is given.